Today's semiconductor devices often comprise multiple layers of metal. Semiconductor place-and-route (P&R) tools are used to place and connect logical blocks (also referred to as cells) of circuit designs. During the P&R process, the resolution of the wires on the semiconductor device and spacing between wires must be considered, and a number of challenges exist.
Diffraction of light used in photolithography has a negative impact on the resolution of the wires that are manufactured. Generally, the smaller the wavelength of the light, the less severe the negative effects of diffraction. As circuits become more complex, the density of cells increases, and the size of the wires decreases. Consequently, the wavelength of the light source used in lithography also needs to decrease to meet the required resolution. Moreover, the light source must provide adequate intensity. In practice, however, the number of viable low wavelength light sources that also provide adequate intensity is limited. Because semiconductor manufacturing equipment is expensive, it is often not economical to replace existing light sources on the installed base of semiconductor manufacturing equipment. In addition, there must be adequate spacing between distinct wires, so that any imprecision in the resolution of the wires would not result in wires becoming disconnected or connected inadvertently.